The present invention relates to a carburetor for an internal combustion engine in which two different fuels are selectively used.
In some automotive vehicles, internal combustion engines are designed to use selectively two fuels such as gasoline and LPG according to the operational conditions of the engines. For example, when large outputs from the engines are required, gasoline is used. When fuel costs or consumptions are particularly regarded, LPG is used.
In such type engines, an induction passage is equipped with a carburetor portion for gasoline and a carburetor portion for LPG. A fuel passage leading to the gasoline carburetor portion and a fuel passage leading to the LPG carburetor portion are controlled to be selectively opened or closed so that either of the two fuels can be supplied into the engine.
However, in such type prior art carburetors, a proper air-fuel mixing ratio cannot be easily obtained. Even after the fuel passage leading to the LPG carburetor portion is opened, the gasoline which remains in the float chamber upstream of the fuel regulating valve in the passage leading to the gasoline carburetor portion continues to be supplied into the induction passage leading to the engine. Thus, both gasoline and LPG are fed at the same time so that the air-fuel mixture is enriched too much. As a result, the operability of the engine is decreased. In particular during engine idling, the engine sometimes stops due to such improper air-fuel mixing ratio.